Stitchbonded fabrics and methods for producing them are known, as for example from K. W. Bahlo, “New Fabrics without Weaving” Papers of the American Association for Textile Technology, Inc. pp. 51-54 (November 1965). Such fabrics are made by multi-needle stitching of various fibrous substrates with elastic or non-elastic yarns, as disclosed, for example, by the Zafiroglu in U.S. Pat. Nos. 4,704,321, 4,737,394 and 4,773,328.
Stitchbonded fabrics are versatile and have a wide variety of applications. Some fabric products, for example, covers for furniture, in particular mattress covers, call for the fabric to have good stretch and/or elastic stretch characteristics. Stitchbonded fabrics could be useful in such applications, however, many traditional stitchbonded fabrics have inadequate stretch capability. Customary stitchbonded fabrics typically have a plain and monotonously uniform appearance that can detract from a product's aesthetic appeal.
To improve stitchbonded fabric stretch, the incorporation of elastic stitching yarns has been used. Despite stitching with elastic yarns and gathering the stitched fabric in both machine direction (“MD”) and cross direction (“XD”) the amount of stretch of the gathered fabric has been limited. The limitations may result from the limited ability of the stitching yarns to stretch, constraint of the stitching pattern or, in respect to nonwoven substrates particularly, from the degrees of alignment and bonding of the substrate fibers. Stitching pattern limits stretch because the characteristic yarn angle of a stitchbonded fabric stitching pattern affects elongation. Yarn angle can depend upon the stitching thread counts per inch, the pattern notation, and spaces between adjacent stitches in the yarn notation. As concerns nonwoven substrate structures, parallel alignment of the fibers to high degrees (in the MD) tends to limit MD elongation and to promote fabric failure at low cross direction elongation when the nonwoven fibers are bonded to a relatively high degree. If the nonwoven fibers are aligned parallel to a lesser degree some additional XD stretch occurs but extension is limited by the interfiber bonding.
A technique known as “weft insertion” has been developed which can provide increased cross directional stretch of stitchbonded fabrics. This method entails placing weft yarns having very favorable elastic properties across the substrate layer at a location just ahead of the needle bed of the stitchbonding operation, typically with a creel system. Such a system takes yarn from a package and mechanically throws it across the substrate. A conveyor system oriented in the fabric cross direction advances toward the needle bed while holding the weft yarns in place until immediately before the yarns enter the needle bed. There the conveyor releases the entering yarn letting the warp yarns overstitch and lock the inserted wefts in place. This provides a high degree of cross directionality to the yarn and allows the resulting stitchbonded fabric to take good advantage of the yarns stretch and recovery properties. Stretch of the weft-inserted stitchbond fabric still is constrained by elastic-limiting characteristics of the underlying substrate sheet and by the overstitched pattern used to maintain inserted weft position.
Selected advances in technology of stitchbonded fabrics are documented in many patents including those of D. Zafiroglu which are presently assigned to Xymid, L. L. C., such as U.S. Pat. Nos. 4,773,238; 4,876,128; 4,998,421; 5,041,255; 5,187,952; 5,247,893; 5,203,186; 5,308,674; 5,879,779; 6,407,018; 6,821,601; and 6,908,664.
A noteworthy utility for stitchbonded fabrics having desirable XD elongation and especially elastic XD elongation is that of skirts for mattress covers. A mattress cover skirt is a band of typically stretchable fabric attached to the periphery of and suspended downward from a top panel that covers the surface of the mattress. Usually the skirt is configured such that its MD is aligned with the periphery of the panel and XD corresponds to the normally narrower width of the skirt. The skirt may have some decorative function but mainly it stretches elastically to effectively hold the cover in place on the mattress. It is desirable to have mattress cover skirts with good cross direction as well as machine direction stretch properties.
Many inventions pertaining to cover skirt technology are disclosed in various patents now assigned to Xymid, L. L. C., such as U.S. Pat. Nos. 5,636,393; 5,603,132; 6,199,231; 6,272,701; 6,842,921; and 6,883,193. The entire disclosures of all U.S. patent and patent applications identified herein are hereby incorporated by reference herein.
In addition to stretch, conventional stitchbonded fabrics can be constrained within other narrow performance parameter ranges by the use of a substrate layer that has uniform physical properties over the entire extent of the fabric. Representative physical properties that are uniform throughout the substrate layer in a traditional stitchbonded fabrics include density, composition, basis weight, thickness, porosity, chemical resistance, and texture to name a few. Because the properties of the substrate layer are the same everywhere in the fabric after stitching, the overall fabric necessarily is confined within a performance range dictated by the substrate component characteristics.
One particularly dramatic example of a limitation on the ability of a stitchbonded fabric to perform relates to the substrate layer density. Occasionally fabric designers desire to have a stitchbonded fabric that employs an extremely low density nonwoven substrate layer. In simplest terms stitchbonded fabrics are made by passing the substrate layer material usually continously through a stitching machine typically having plural needle bars each having multiple guides threaded with the stitching yarn. The substrate material is usually unwound from a supply roll and appropriately tensioned and guided by additional rolls and mechanisms for alignment and speed control. If the density of the substrate is too low, it lacks the stiffness and integrity to stand up to the unwinding and other operations preparatory to feeding into the machine. The substrate can also be too flimsy to be stitched. Consequently, the fabric with such a low density substrate cannot even be manufactured. As will be explained below, it has now been discovered that a stitchbonded fabric can be made with a substrate layer comprising regions of different density. In a particularly effective embodiment, a substrate layer having regions of ultra low density substrate along with other regions having higher density can be successfully fed to the stitchbonding machine such that the average density is very low. This novel technique can solve the problem of making very low density substrate layer stitchbonded fabrics which could not otherwise be easily fabricated in conventional machinery.
It is desirable to have a stitchbonded fabric that provides high stretch and and optionally elastic stretch especially in the cross direction. A stitchbonded fabric having superior stretch and which is simple to manufacture with only minor modifications to conventional stitchbonding equipment is also much desired. There also is a need for making a stitchbonded fabric stretchable in an aesthetically pleasing manner and with overall strength and structural integrity. Yet further there is a desire to have a stitchbonded fabric that advantageously provides physical properties which are different in different regions of the fabric. Additionally it is wanted to have stitchbonded fabrics that present highly decorative designs and varied appearance features without resorting to complicated and expensive stitching yarns and stitching patterns.